Electrolytic production of adiponitrile



Dec. 2, 1969 D. D. DAVIS 3,481,846

ELECTROLYTIC PRODUCTION OF AD IPONITRILE Filed June 24, 1963 INVENTOR DARWIN DARRELL DAVIS BY MXi ATTORNEY United States Patent M 3,481,846 ELECTROLYTIC PRODUCTION OF ADIPONITRILE Darwin Darrell Davis, Orange, Tex., assignor to E. I. du Pout de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed June 24, 1963, Ser. No. 290,112 Int. Cl. C07c 121/06, 121/26 US. Cl. 204--74 6 Claims ABSTRACT OF THE DISCLOSURE Process for producing adiponitrile comprising passing a direct electric current through an electrolyte containing acrylonitrile, lithium bromide and water.

This invention relates to the production of adiponitrile from acrylonitrile. Specifically, this invention relates to the production of adiponitrile by passing a direct electric Current through an electrolyte containing acrylonitrile using lithium bromide as the conductive compound in the electrolyte.

It is known that acrylonitrile can be reacted to produce adiponitrile by means of potassium amalgam which is produced electrolytically. The amalgam then reacts chemically with acrylonitrile and hydrochloric acid to form adiponitrile. It is an object of this invention to provide an alternative process for the production of adiponitrile from acrylonitrile which does not require the use of amalgam. Other objects of this invention will be apparent to one skilled in the art from the remainder of the specification.

The above objects are accomplished according to the present invention by passing a direct electric current through acrylonitrile containing from about 1 to about 3.8% by weight water and lithium bromide. The process of this invention may be carried out with or without a diaphragm in the electrolytic cell. If a diaphragm is to be used, it is preferable to employ a cationic permselective membrane (that is, a membrane that is only cationpermeable). Such diaphragms are known in the art and are commercially available. If a cationic permselective membrane is used, an anolyte may be employed that contains no acrylonitrile. This can be advantageous for under some conditions the anodic oxidation products tend to couse polymerization of the acrylonitrile. However, a diaphragm is not necessary to the successful operation of the process of this invention.

In the drawings, FIGURE 1 shows a cross-sectional view through a diaphragmed electrolytic cell suitable for use in carrying out the process of the present invention.

FIGURE 2 shows a cross-sectional view through an electrolytic cell without a diaphragm that is suitable for carrying out the process of the present invention.

The process of the present invention is carried out at a cathode current density between about 50 and about 200 amps] sq. ft. and at a voltage (cathode to anode) of between about 1.2 and 15.0 volts. The process is preferably carried out within the temperature range of 30 to 70 C. because the conductivity of the electrolyte is greatest at this temperature. The optimum temperature is about 45 C. The pH of the system is critical only in that the pH should be on the acid side, i.e., less than 6. The concentration of the lithium bromide in the moist acrylonitrile can vary over wide limits, but about 2 to about 8% is satisfactory in most instances. The concentrations of about 3 to about 7% are preferred.

It is highly desirable, when carrying out the process of this invention, in either an undiaphragmed cell or in 3,481,846 Patented Dec. 2, 1 969 a diaphragmed cell to agitate the portion of the cell in which the acrylonitrile is undergoing hydrodimerization. Agitation avoids areas of high pH and reduces the degree of polarization, resulting in increased yields. The degree of agitation useful in the present process varies with the applied cathode current density, but is generally from a Reynolds number of about 12,000 to about 200,000, preferably about 100,000 to about 175,000.

When the process of this invention is carried out in a diaphragmed cell, the diaphragm is preferably a cation permselective diaphragm. Suitable ion exchange membranes are commercially available. Useful membranes can be made by sulfonating a copolymer of styrene and divinyl benzene, and blending the product with polyethylene. The blend is then formed into a sheet of about .045 inch thickness. Sulfonated copolymers of styrene and divinyl benzene may be ground and blended with sulfonated polyethylene and cemented as a sheet to Dynel (a copolymer of vinyl chloride and acrylonitrile). Some membranes require pre-soaking prior to use. This can be accomplished by techniques known in the art, for example the membrane is installed in the cell, and then treated with aqueous H 50 (5%). This treatment avoids uneven swelling and buckling. The anolyte in the diaphragmed cell is an aqueous acid. Sulfuric acid at a concentration of about 25 to 45% is highly satisfactory. Also, dilute hydrobromic can be used when satisfactory means are available for removal of the bromine. Aqueous organic acids, such as ethyl sulfuric acid and p-toluene sulfonic acid are also satisfactory. Weak acids, such as formic and hydroiodic, give relatively poor results.

Cathode materials suitable for the process include lead, platinum, palladium, copper, nickel, chromium on brass, and silver. Platinum, lead, silver and copper are the preferred cathode materials. The anode may be of any relatively inert conductor; platium and carbon are highly satisfactory.

The catholyte, or in the case of an undiaphragmed cell, the electrolyte, may contain (in addition to acrylonitrile, water, and lithium bromide) other materials that do not substantially affect the basic composition. For example, cosolvents for the lithium bromide, may be included. Specifically, dimethyl formamide, methanol, 0r isopropanol may be added to the catholyte as cosolvents for the lithium bromide.

When carrying out the process of this invention for extended periods of time, it is usually desirable to periodically or continuously add acid, such as sulfuric or hydrobromic, to the electrolyte in order to maintain the pH below 6.

The drawings diagrammatically illustrate alternative apparatus suitable for carrying out the process. FIGURE 1 shows an electrolytic cell designated 1, having a cathode 2 in catholyte 3, and an anode 4 in anolyte 5. The anolyte and the catholyte are separated by a cation permselective diaphragm 6. The cathode compartment of the cell contains an agitator 7. Suitable inlet means 8 and outlet means 9 are provided for the cathode compartment. The anode compartment has inlet means 10 and outlet means 11. The cell is also provided with suitable vents 12 and 13 to remove the gaseous electrolytic products. FIGURE 2 diagrammatically shows an undiaphragmed electrolytic cell suitable for use in the process of this invention. The cell 1 is provided with a cathode 2, an anode 4, an agitator 7, an inlet means 8 an outlet means 9, and vents 12 and 13. Additionally, inlet means 14 is provided to allow the introduction of acid to keep the pH acidic.

In operation either of the cells may be run in a batchwise fashion or continuously. That is, electrolyte (moist acrylonitrile and lithium bromide) may be introduced continuously through inlet 8 and withdrawn continuously through outlet 9; or the electrolyte may be introduced through inlet 8, electrolyzed and withdrawn as a batch through outlet 9. In either instance, the adiponitrile is separated from the acrylonitrile, water, and lithium bromide by further processing after removal through outlet 9.

In the following examples which illustrate the invention, all parts and percentages are in parts by weight unless otherwise stated.

EXAMPLE I In a cell, such as illustrated in FIGURE 2, an electrolyte consisting of 79 parts of acrylonitrile, 14.1 parts of dimethylformamide (a cosolvent for the lithium bromide), 3.5 parts lithium bromide, and 3.4 parts water was electrolyzed with mild agitation using a cathode current density of 60 amps/sq. ft. for 90 minutes, using a lead cathode and a platinum anode. Hydrogen gas was introduced in the anode region in an effort to minimize the polarization. The pH of the electrolyte averaged about 0.8. The product was removed and analyzed, and the current efiiciency for the production of adiponitrile was calculated to be 14%.

EXAMPLE II Into the cathode compartment of a cell having a diaphragm of Amberplex C-l (an ion exchange membrane made by blending a sulfonated copolymer of styrene and divinyl benzene with polyethylene, and then forming a sheet of the blend), 79 parts of acrylonitrile, 14.1 parts of dimethylformamide, 3.5 parts of lithium bromide, and 3.4 parts of water were introduced. Into the cathode compartment a 30% by weight aqueous solution of hydrobromic acid was simultaneously introduced. The membrane had an area of approximately 0.024 sq. ft. The membrane had a thickness of approximately 0.045 inch. The cathode was vigorously agitated by means of a stirrer and voltage of aproximately 8 volts was applied between a platinum anode and platinum cathode for about 90 minutes. The cathode current density was about 50 amps/sq. ft. The temperature was approximately 30, and the pH was about 1. The current efficiency was about 14% calculated with regard to the amount of acrylonitrile converted to adiponitrile.

The products of the above examples were purified and analyzed by the following process:

The pH of the organic product from the electrolytic cell was adjusted to 3.5-4.5 and then filtered. The filter cake Was discarded. The organic liquid was extracted with water and methylene dichloride, the water washes being extracted with methylene dichloride and the methylene dichloride extract being washed with water. The aqueous layers were consolidated at the end of the extraction, and the organic layers were separately consolidated. The Water was stripped from the combined aqueous layers, leaving as a product dried lithium bromide.

The combined organic layers were charged slowly through a separatory funnel into the distillation apparatus flashing the acrylonitrile and CH Cl on over a steam bath. The separatory tunnel was then removed, and a thermometer was installed where the separatory funnel had been and the distillation resumed at 40 mm. Hg for about five minutes after visible boiling had ceased. The pressure was then decreased to mm. Hg, and distillation continued until a pot temperature of 70 C. was reached. The adiponitrile was then recovered by distillation.

In the foregoing examples the current efiiciency to adiponitril is the percentage of the current which is utilized in making adiponitrile. By-products included hydrogen gas, propionitrile, beta-hydroxy propionitrile and beta, beta-oxydipropionitrile, and polyacrylonitrile. The current efiiciency can be determined as exemplified by the following sample calculation. In a run in which the average current is 2.8 amps. and the duration is 156 minutes, the current density is 2.8 l56 60=26,200 amp.-sec. or 0.2720 faraday. If the electrolyte weighs 252 grams and has a concentration of4.27% adiponitrile, the quantity of adiponitrile is 0.10 mol, and at two faradays per mol of adiponitrile the current efiiciency to adiponitrile is 0.10/ 0.2720 2 which is The adiponitrile produced by the disclosed process is useful as an intermediate in the production of nylon.

I claim:

1. A process for the production of adiponitrile which comprises passing a direct electric current at a potential between about 1.2 and 15 volts at a cathode current density between about 50 and 200 amps/sq. ft. between a cathode selected from the class consisting of palladium, nickel, chromium on brass, platinum, lead, silver and copper, and an inert anode through an electrolyte, in contact with said cathode, consisting essentially of acrylonitrile, about 2 to about 8% lithium bromide, and between about 1 and about 3.8% water thereby forming adiponitrile and thereafter recovering the adipontrile, said electrolyte having a pH of less than 6.

2. The process of claim 1 in which the anode and the cathode are separated by a membrane that is cation permselective.

3. The process of claim 2 in which the anode is surrounded by an aqueous acid electrolyte.

4. A process for the production of adiponitrile in an electrolytic cell having an anode compartment and a cathode compartment, said anode compartment being separated from said cathode compartment by means of a cationic permselective membrane, which comprises subjecting an electrolyte consisting essentially of acrylonitrile containing between about 1 and about 3.8% water and about 2 to about 8% lithium bromide to the action of direct electric current in the cathode compartment of said cell thereby forming adiponitrile and thereafter recovering the adiponitrile.

5. The process of claim 4 in which the anode compartment of said cell contains an aqueous acid solution selected from the class consisting of sulfuric acid, hydrobromic acid, ethyl sulfuric, and p-toluene sulfonic.

6. A process for the production of adiponitrile in an electrolytic cell having an anode compartment and a cathode compartment, said anode compartment being separated from said cathode compartment by means of a cationic permselective membrane, which comprises subjecting an electrolyte in the cell to the action of direct electric current, the electrolyte in the cathode compartment consisting essentially of between about 1 and about 3.8% water, between about 2 to about 8% lithium bromide and acrylonitrile, whereby adipontrile is formed in the cathrode compartment of the cell, and recovering adiponitrile.

References Cited UNITED STATES PATENTS 2,726,204 12/1955 Park et al 204-72 3,193,480 7/1965 Baizer et al 204-73 3,193,481 7/ 1965 Baizer 204-73 FOREIGN PATENTS 566,274 11/1958 Canada.

JOHN H. MACK, Primary Examiner H. M. FLOURNQY, Assistant Examiner 

